1. Field of the Invention
The present invention relates to a lens barrel that drives a lens moving portion using a voice coil motor for use in an optical apparatus such as a digital camera or digital video camera.
2. Description of the Related Art
In recent years, the image quality of digital cameras and video cameras has been improved, their prices have been lowered and their sizes have been made smaller. Lens barrels built in cameras are also required to be manufactured with higher precision to improve optical performance and achieve high image quality at lower cost and to be made small.
In lens barrels of optical apparatuses such as digital cameras, a voice coil motor is used as an actuator that drives a lens holding member during zooming or focusing.
FIG. 6 shows the basic structure of a voice coil motor, which includes a magnet 1, yoke 2 and a coil 3. The yoke 2 has a looped shape inside which a magnet 1 is provided. A part of the yoke 2 is passing inside the coil 3 having an annular shape. Magnetic fluxes of the magnet 1 are perpendicular to the axial direction of the coil 3, and the yoke 2 forms a closed magnetic circuit through which magnetic fluxes flow. When a current flows in the coil 3, a Lorentz force associated with the magnetic fluxes of the magnet 1 is generated, and the coil 3 is subjected to a force in the axial direction.
FIG. 7 is a perspective view of a lens holding member that is driven by this voice coil motor. The coil 3 is provided on a lens holding member 5 that holds a lens 4, and the magnetic circuit element including the magnet 1 and the yoke 2 is provided on a fixed member such as an outer barrel that is not shown in the drawings. When the coil 3 is energized, a Lorentz force associated with the magnetic fluxes of the magnet 1 acts in the optical axis direction, so that the lens holding member 5 is subjected to a force in the optical axis direction.
In the lens holding member 5, a sleeve 5a is supported on a guide bar 6a having an axis parallel to the optical axis, and a bearing 5b is supported on a guide bar 6b. The direction of movement of the lens holding member 5 is restricted to the forward and backward directions along the optical axis. Thus, when the lens holding member 5 is subjected to a force in the optical axis direction, the lens holding member 5 moves relative to the outer barrel on which the magnetic circuit element is mounted, so that the lens 4 held by the lens holding member 5 is moved.
Since the direction of the Lorentz force can be switched between the forward and backward directions of the optical axis by changing the direction of the current supplied to the coil 3, the lens holding member 5 can be moved in the forward and backward directions along the optical axis. With the above structure, the lens barrel controls driving of the lens holding member 5 in zooming and focusing operations of the optical system.
In the above described bearing-sleeve-and-bar structure constituted by the lens holding member 5 and the guide bar 6a, if fitting play that deteriorates operation performance occurs, the precision of operation of the lens holding member 5 deteriorates. However, to ensure operation of the lens holding member 5 while taking into account temperature conditions as well, the fitting play should not be eliminated completely. The play will cause displacement of the lens 4 held by the lens holding member 5 in a plane perpendicular to the optical axis and tilt of the lens relative to the optical axis. To avoid such deterioration of performance as much as possible, it is necessary to reduce the fitting play as much as possible or to separately provide a conventional mechanism for removing the play.
Japanese Utility Model Application Laid-Open No. H05-90418 discloses such a mechanism for removing the play. FIG. 8 is a perspective view of this mechanism, in which a lens holding member 12 that holds a lens 11 is supported by a basic guide bar 13 and a rotation regulation guide bar 14. The lens holding member 12 is adapted to be capable of sliding in the optical axis direction. The basic guide bar 13 made of a magnetic material is passing through guide holes 12b (one of which is not shown in FIG. 8) formed on a bearing portion 12a provided in the lens holding portion 12. Magnet members 15a, 15b are embedded above the guide holes 12b. The lens holding member 12 is always biased in a direction transverse to the basic guide bar 13 by attraction force of the magnet members 15a, 15b. Thus, the play between the lens holding member 12 and the basic guide bar 13 is removed.
However, providing an additional mechanism like the conventional art shown in FIG. 8 to remove the play leads to an increase in the number of parts and complexity of the structure and assembly, which makes the cost higher and prevents downsizing of the lens barrel due to an increase in the space required to accommodate the parts.
An object of the present invention is to eliminate the above described problems and to provide a lens barrel in which the fitting play that hampers precision of the lens barrel is removed by using a small number of parts.